Beta2Agonist

Beta-2 agonists are a class of medications that selectively stimulate beta-2 adrenergic receptors. Activation of these receptors on bronchial smooth muscle leads to relaxation and bronchodilation, increasing airway caliber. Beta-2 receptors are also present in other tissues, and stimulation can produce tremor and vasodilation, with metabolic effects mediated by increased cyclic AMP (cAMP). At higher systemic concentrations, modest cardiac effects may occur.

Pharmacology and mechanism of action involve activation of Gs proteins and adenylate cyclase, raising intracellular cAMP. This promotes relaxation of airway smooth muscle and can stabilize mast cells, reducing mediator release. The resulting bronchodilation improves airflow and symptoms in obstructive airway diseases.

Clinical use includes relief of acute bronchospasm and maintenance therapy for asthma and COPD. Short-acting beta-2 agonists (SABAs), such as albuterol (salbutamol), provide rapid, temporary relief of symptoms. Long-acting beta-2 agonists (LABAs), such as salmeterol and formoterol, provide sustained bronchodilation for at least 12 hours and are commonly used for maintenance therapy, usually in combination with inhaled corticosteroids in asthma. In COPD, LABAs can be used alone or with muscarinic antagonists. Terbutaline, a beta-2 agonist, has been used as a tocolytic in preterm labor, though its use is restricted by safety concerns.

Administration is typically inhaled to maximize lung effects while minimizing systemic exposure; oral or intravenous forms exist but carry higher risk of systemic adverse effects. Common adverse effects include tachycardia, tremor, palpitations, headache, hypokalemia, and hyperglycemia. There is a risk of paradoxical bronchospasm. Beta-2 agonists may interact with monoamine oxidase inhibitors and certain antidepressants, increasing effects. In asthma, LABAs should be used with inhaled corticosteroids and not as monotherapy.